Integrated circuits (ICs) are commonly used in various electronic systems, including computer-based systems, logic based systems, control systems, and other systems known in the art. During production and manufacturing of these systems, ICs may remain unused (e.s. in inventory) for extended periods of time, where they can be exposed to environmental conditions, such as, humidity and moisture. The moisture typically can be in the form of water vapor in air. Exposure to moisture typically can occur during production downtime, for example, during production “change-overs” or during small quantity production of an electronic system, where continuous production is not required. Of course, exposure to the elements, such as moisture, may also occur during other production downtime events, which are experienced in conventional manufacturing and assembly operations.
Each IC includes a silicon device within a mold, typically formed of a plastic material. Each IC has a corresponding moisture sensitivity level with an associated maximum exposure time. The sensitivity levels and exposure times, as well as, staying the maximum exposure time, have associated industry standard requirements. When an IC has exceeded an industry standard requirement, the IC is typically discarded or baked for an extended period of time. Discarding of ICs, causes wasted expense and baking of ICs can have associated disadvantages, as stated in detail below.
A typical series of manufacturing steps, for an electronic system, stated above, are as follows. First, a tape reel or tray of ICs is removed from an airtight moisture barrier bag, for use in an assembly machine. Once the bag is opened to begin manufacturing, the components have a limited useful life. Next, The ICs are placed onto a printed circuit board having a solder paste pattern to form an electronic system assembly. Finally, the electronic system assembly is placed into a reflow oven, to melt the solder and form solder bonds between the ICs and the printed circuit board.
ICs that have been exposed for extended periods of time to levels of moisture typically found in air at most production and manufacturing facilities, are vulnerable to internal damage when processed in a reflow oven. This vulnerability requires special handling methods that increase manufacturing costs.
When an IC is exposed to moisture, a moisture permeating process begins. Moisture penetrates into the mold and gradually reaches a center cavity, where the IC resides therein. When the IC is baked, due to the moisture level of the molding compound, delamination of mold from the silicon device can occur, with consequent breaking of wire bonds. The broken wire bonds cause intermittence during post assembly operating use of the IC. Although ICs are tested upon completion of assembly before being used as intended, the delamination may be undetectable, since the silicon device wire bonds may be resting on or touching silicon device contacts even though a wire bond no longer exists.
An IC maximum exposure time can be stayed using several methods. A first method includes placing the IC in a “Dry Box”, which prevents further exposure to moisture, during downtime. A disadvantage with the dry box is that the moisture that previously entered the IC, remains in the IC, which may cause operating intermittence. Also, potential future industry standards, prohibiting the use of dry-boxes, may be introduced due to the potential associated intermittence. Another method includes baking the IC for a period of time to remove moisture that has entered the mold. By baking the IC, the moisture penetration process is reversed. Obviously, this baking is time consuming, not cost effective, and can cause oxydation of solder coating on IC leads, degrading the ability to have a solder joint formed to the IC. As another method, the ICs can be reinserted into moisture barrier bags, during downtime, although is also time consuming and requires a supply of moisture barrier bags and desiccant material, as well as a sealing apparatus.
It would therefore be desirable to develop a method of reducing the amount of moisture exposure of ICs during manufacturing and production processes, which does not require special handling and is cost effective.